If, like me, you need to stitch together cropped EXR files in PS 6 (I don't know if this applies to later versions of PS), there's a gotcha that I just stumbled across that you might like to know about. I had always assumed that if you trimmed off the black and resaved the crop as a new EXR, that the full range of tonal values present in the original EXR file would be preserved. Not so. Unfortunately, if there are any blown highlights in the exposure of the original file, the new EXR will lose any further tonal information in the blown area, even if you subsequently reduce the exposure. The solution? You have to make sure that the original file is exposed at a low enough value that no highlights are blown - then the new EXR made from it is fine.
Just to illustrate: the first image was made from an original exposure set at 0, then saved as a new EXR and then re-exposed at -3 -result, blown highlights. The second image was made from the same original exposure set at -3, then re-exposed again at -3.
